1. Field of the Invention
This invention relates to an improved process for the manufacture of 1,2-dibromo-2,4-dicyanobutane.
2. Reported Developments
1,2-dibromo-2,4-dicyanobutane is well known in the prior art and is being sold as MERGUARD(copyright) 1200 by Calgon and as INTEGRA(copyright) CG-20 by International Specialty Products, Inc. The compound, also known as 2-bromo-2-bromomethylglutaronitrile, exhibits excellent preservative activity in use in compositions of personal care, nutritional and pharmaceutical products. It is produced by several methods, using the technique of bromination of 2-methyleneglutaronitrile, as described, for example, in U.S. Pat. Nos. 3,929,858, 3,877,922, 3,849,422, 3,873,597, 3,833,731 and 3,644,380.
Purification to eliminate coloration and irritating odor is described in U.S. Pat. No. 4,504,423.
Generally characterized, the prior art describes the addition of excess bromine to a suspension of 2-methyleneglutaronitrile at high temperatures. The reaction is completed in about 4 to 8 hours. The excess bromine is decomposed. On cooling, the reaction mixture is solidified, filtered, and washed repeatedly with water and sodium carbonate or a nitrate solution. The product is then recrystallized from an alcohol, such as methanol, and isolated in one or two crops.
Some disadvantages have been observed with the product made by some of the disclosed processes including the following.
In all cases at least 2-3 unit operations are involved; the reaction is heterogeneous; higher operating temperatures are required to complete the reaction in a reasonable time; the process train requires specialized reactors, centrifuges and driers to constrain corrosion; in most cases the upper aqueous layer that is highly acidic needs to be decanted off; which is industrially unfeasible; and the recrystallization process requires, sometimes in two crops, additional equipment and time.
Accordingly, it is an object of the present invention to provide a process to prepare 1,2-dibromo-2,4-dicyanobutane which avoids these and other disadvantages and produces a solid form of the compound free of any color and irritating odor.
The improved process of the present invention comprises:
mixing 2-methyleneglutaronitrile with a polar, non-aqueous alcoholic solvent selected from the group consisting of methanol, ethanol, and isopropanol to obtain a solution;
gradually adding bromine to the solution and carrying out the reaction at about 25xc2x0 C. to about 65xc2x0 C., and preferably at about 30xc2x0 C.;
neutralizing the solution with a 5% sodium bicarbonate solution to neutral pH;
adding water to the solution while cooling to precipitate;
filtering and washing the product; and
drying the product under vacuum at low temperatures.
In reacting 2-methyleneglutaronitrile with bromine, 1 to 2 mole % less of bromine is used to insure that no free bromine is present at the completion of the reaction.
The final product is a white crystalline solid that is free of discoloration and irritating odor even on drying and extended storage.